The present invention relates to a process for manufacturing articles of filter paper, the process including the formation of weak points as a result of mechanical working, and strengthening the paper with the aid of a wet-strength increasing agent (wet strengthener) of cross-linked cationic polyalkylenimines.
In the past, these articles have been manufactured by adding the wet strengthener in the pulping engine as well as in the mixing tub during the production of the filter paper so as to increase the wet strength of the material.
With this manner of proceeding, the wet strength can be increased, with the maximum permissible dosage, by about 30 to 35% compared to untreated filter paper. Addition of more strengthener does not result in significant increases in wet strength, but adversely influences the filtrability of the paper.
Depending on the shape of the articles made of the filter paper, mechanical working produces weak points in the paper, e.g. the knurling on filter paper inserts by relief printing or the edge region reinforcement and perforation of filter paper panels. The high stamping pressure applied then results not only in excessive wear of the stamping tool but particularly also in considerable crushing of the seam area and thus in the formation of considerable amounts of weak points.